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Tracking a radiation trail in space

In my story an unknown energy source enters the solar system, as it speeds towards the inner planets it leaves behind a radioactive trace/trail. Think of the wake left behind by a speedboat. What equipment (ideally both on Earth and in space) could detect this radiation? I know they can't track it in real time, but I can't identify a piece of equipment that would detect and record this trail of radioactive energy speeding across the solar system. The concentration and beam like properties of the radiation would be evidence of intelligence, not just background space radiation.

Can anybody help? The best I've found is a gamma radiation telescope, would this do the job I need it to.

So a radio telescope can still detect radiation because they both fall into the electromagnetic spectrum? Wish I was more knowledgeable in this area!

The actual signal is an unknown energy source (lazy writing I know, but it is coming from an extra-terrestrial source, and that's the same level of detail Arthur C Clarke gave about the transmission the monolith sent to Jupiter). The radioactivity is the by-product of the signal - so I guess the type would be determined by this. Basically one which is easiest to detect, with limited equipment. I'm leading towards gamma, as it's exotic enough to be in a sci-fi story and detectable enough because there is a telescope that already does that...

Just a note: radiation doesn't really form trails, as such. Especially gamma. It's just a form of light, so it's not so much like the wake of a speedboat as it is a lamp on the back of that boat. This means that there's no twists and turns; it just points to where the thing is (or was, what with light taking a long time to cross the huge distances of space). If you want a trail, like speedboat wakes or tyre tracks, then you'll need to have them follow the trail of exhaust (which might itself be radioactive).

I think that it would depend on the amount of energy and how it was given off. If it was just emitted randomly and in a small amount, then it would be difficult to detecteven immediately after. Butm if the radiation was generally directional and in great quantity, then it would affect the surroundings as it passed. There might be a small increase in temperature, and some materials probably would absorb and re-emit energy, so there might be a secondary radiation.

The exact wavelength is unimportant, because there is energy at every wavelength. That a source had emitted it in a line across an expanse would be very significant.

1. As Anaximander mentioned, radiation doesn't form trails; it's generally straight-line emission from the radioactive source - like light from a light bulb. So if you wanted a radiation trail, what you'd probably need is a trail of material/waste/debris that was itself radioactive.

2. There are different kinds of radiation. Just for starters, there's both particle and electromagnetic radiation. Particle includes neutron, alpha and beta radiation; e-m includes gamma and X-ray radiation. They have different effects, are caused by different things, and are detected with different instruments.

3. Even if your characters don't know the nature of the energy source, you should have some idea about it. At the very least, read the Wikipedia entry on Radiation.

"Crazy visions you got. Come with me to barber, we bleed you, you see right, everything good. I buy for you first leech."- The Wrong Sword

Radiation can also be emitted spherically (as from a star or a heat source, for example).

You can get a wake of radiation if you have a moving source that emits radiation away from it (either linearly or radially). As it moves the radiation will spread off to the sides in a pattern pretty similar to a wake.

By unknown energy source do you mean unknown source of energy or source of unknown energy?

The former can be characterized by producing sets of particles that don't as far as we know tend to appear together. The latter is tricky. Detecting what you don't know about is kind of difficult. You usually need some side effect that is acting in an unusual fashion. Which is presumably what you want the radiation trail for.

Radiation can also be emitted spherically (as from a star or a heat source, for example).

You can get a wake of radiation if you have a moving source that emits radiation away from it (either linearly or radially). As it moves the radiation will spread off to the sides in a pattern pretty similar to a wake.

This is mostly true. However, the effect is less like a ship's wake than might be required - by the sound of it, what's needed is a trail that can be followed later, but an expanding "shell" of radiation as you describe wouldn't do this. The effect you describe would (from a stationary viewpoint) would result in a moving "light", something like watching someone wave a torch around. You could draw the path (and persistence of vision does this for you) but at any given instant there will be a single point. A trail of radioactive exhaust is probably your best bet for something you can follow at a later date.

Neutron Sniffer. Manufactured by Alecon Industries. Able to track starships through hyperspace. Detects signature radiation from engine exhaust. Each engine has a distinct exhaust signature, much the same as today's submariner sonar can detect the specific marine engines by their sounds.